For the best equipment, the Tisiphone Edge (dropped by Cruel Dragons) is only the best weapon a couple of characters like Jenna IIRC. For spellcasters like Sheba, you can get the Lachesis' Rule from the Mad Demons in Anemos Sanctum. For pure fighters like Felix, the best overall weapon is the Excalibur, but you'll need Orihalcon (and a lot of luck) to get it. Orihalcons are randomly dropped by Sky Dragons, that're also found in the Anemos Sanctum. Besides this, the Orihalcon can be used to forge the best armor in the game, the Xylion Armor, meaning you'll probably need a lot of them. The best helm in the game for Garet and Felix is found in the final dungeon, it's called the Gloria Helm and it's dropped by those blue variations of the Druj (the monster that drops the Berserker Armband). There are a few others, but I can't recall all of them, it's been 3 months since I last played the game. I reached this point where I killed Dullahan with pure physical attacks and finally got sick of it.

As I said, it's been quite a while since I last played the game, I'm just pulling everything off the top of my head instead of reading up an FAQ. I just remembered though that the best arm equipment in the game is the Riot Gloves, which is dropped by those minotaur monsters in the hidden cave in the desert. And the Darksword is far from the best weapon in the game. It's a cursed weapon and unless you're equipped with a Cleric Ring, it's going to cause a lot of problems for whoever is using it. In terms of attack power, it's supposed to be the best but its unleash, Abbadon is one of the worst in the game. The Excalibur on the other hand is the best overall weapon even though it only has the 3rd highest attack power after Darksword and Sol Blade, mainly due to the fact that its unleash, Legend, is really easy to pull off and is the most powerful in the game, being able to deal roughly 1500 damage to the final boss in my game if all three hits connect.

Goden sun is a tricky game. Most people get stuck and try everything. Other people get stuck and restart. I got stuck once and stopped playing for 5 months. When I started playing again I beat it soon after.